One significant difference between the imagery and language in Langston Hughes' "The Negro Speaks of Rivers" and Alain Locke's essay "The New Negro" is seen with respect to content and theme. For Hughes' poem, the central theme is about historical roots, while Locke's essay focuses more on new beginnings and a new outlook.
We can clearly see the theme of historical roots in the names of rivers and locations that Hughes states in his poem. The first river he names is the Euphrates, which was central to the establishment of the ancient Babylonian civilization. It flows from Turkey to Syria and then on again through Iraq. Mentioning such a historically significant river serves the purpose of connecting the negro to ancient roots. Next he mentions the Congo, which of course is a central African river, again establishing the negro's roots to Africa. The names of the Mississippi and New Orleans of course connect the negro to their forced, uprooted life in America. In addition to the use of names of rivers as language, sight images such as "I built," "human blood," and "human veins" serve to connect the human negro to the life he/she lived in Africa, again drawing the connection to historical roots.
In contrast, Locke argues that there is an Old Negro and a New Negro. He argues that
for generations ... the [Old] Negro has been more of a formula than a human being--a something to be argued about, condemned or defended, to be "kept down," or "in his place" or "helped up." (p. 4)
More importantly, he argues that the negro is now suddenly moving past this old idea, getting out of the grasp of "tyranny" and "intimidation" and "shaking off the psychology of imitation and implied inferiority" (p. 4). He is essentially arguing that the negro is now establishing his/her own brand new identity. Beyond the language used in the argument to establish the old identity, we further see the idea of newness in images found in a poem he quotes in the same essay, such as in the lines:
We have tomorrow
Bright before us
Like a flame.
Here, the sight images of "bright" and "flame" help to paint the image of a brand new dawn, or rising sun, which is also a symbol of a new day.